1. Field of the Invention
The present invention is directed to conveyor systems, and more particularly to controllers for accumulation conveyors.
2. Description of Related Art
Conveyors are used to transport goods and packages in all types of environments and experience especially heavy use in manufacturing and shipping industries. In addition, characteristics of the flow of goods and packages along such conveyor systems, such as timing and positioning of the goods and packages, must often be tailored to the needs of the manufacturer or shipper. Accumulator conveyor systems are divided into zones in which a driving force may be selectively applied to a conveying surface which provides each package with a stopping position. As a result, packages or goods may be accumulated in successive zones for eventual discharge from the conveyor.
As an example, U.S. Pat. No. 5,862,907 to Taylor (“Taylor”) discloses an accumulation conveyor 10 that is divided into a plurality of accumulating zones A, B, C, D and E, as shown in FIG. 1 of Taylor. The conveyor 10 includes a conveying surface, in this case a plurality of rollers 14, that are selectively driven under the control of a plurality of accumulation modules 20A-E that correspond to the accumulating zones. Each module 20 is capable of communication with its neighboring or adjacent module in the upstream and downstream directions through communications cables 42A-E. Photoelectric or ultrasonic or other types of sensors 28 are used to determine the presence or absence of an item or package within each of the accumulating zones. Thus, when a sensor fails to detect a package in a downstream zone, its module communicates with the upstream zone to activate its conveying surface and convey an object held therein to the downstream zone.
Despite improvements in the control systems of conveyors, conventional conveyors have other areas in which improvements are needed. For instance, problems may be encountered when the packages are not all the same length. Generally, this requires that the conveyor zones be sized to fit the largest packages being conveyed. If the large packages are few, then this results in a large amount of wasted conveyor space because the majority smaller packages do not fill each zone. Since the accumulation conveyor is essentially temporary storage, the reduction in package capacity is not desirable. Also, when the cartons are released a zone-length space is created between the cartons which reduces the throughput capability of the conveyor.
Therefore, it would be advantageous to have a conveyor system that is capable of zero pressure control of accumulation of individual cartons or packages of widely varying length. It would be further advantageous if the conveyor and control system were capable of handling packages of varying length while minimizing losses of accumulation and transportation efficiency.